The extensive use of deicing salts has resulted in penetration of these salts into concrete, with resulting corrosion of steel re-enforcing and even prestressed tendons. The corrosion leads to expansion of the steel re-enforcing with resultant spalling of the concrete above the steel, causing pot holes in the surfaces of bridge decks and parking structures.
The customary way to repair bridge decks has been to repour additional new concrete topping over the deck. This method is not only expensive but in parking structures, there are many times no tolerance for added weight and decreased head room. Pot holes may be repaired with high quality concrete, but it is generally considered that the exposed steel should have a minimum of 1 inch to 11/2 inches of concrete over the steel. If the patch is left exposed, the concrete over the steel should be a minimum of 2 inches thick. Hence, a problem exists when exposed steel re-enforcing is only a small distance below the concrete surface.
In the past, sand filled polymers such as epoxies, methyl methacrylates and polyesters have been used for this purpose. Fiber re-enforced concrete has also been used. In almost all cases, the stress is caused by traffic impact, thermal chances, and other stresses have resulted in subsequent cracking of these materials under usage.
Specifically, there are three preferred prior art methods for concrete patching. One method includes applying new concrete, this method being utilized mostly for deep patches of 1 inch or more. A second method utilized is a mixture of polymer concrete wherein aggregates are mixed with epoxies, polyesters and methyl methacrylates. A third method utilizes inorganic quick set cements of the phosphate and magnesium type which are fast setting and preferably used on bridge decks. The problem with these methods are that the applied patch is rigid when cured and has limited flexibility. Additionally, the thermo-expansion coefficient of the patch in the last two methods is different than that of the concrete. In all three of the prior art methods, the curing of the patch may build up a sizeable exotherm and expand during cure. Upon cooling of the patch, undesirable thermal stresses are created.